Treatment of raw phosphates



A. FOSS ET AL TREATMENT OF RAW PHOSPHATES Filed May 27, 1932 Deoom posilion Cazcihed phosphates Patented Nov. i7, i935 l unire-o STATES .PATENToFFl'CE TREATMENT F RAW PHOSPHATES Antonius Foss, Olaf Jensen, and OddHerbert l Londe, Oslo, Norway, assignors to Norsk Hydro- ElektrlskKvaelstofaktieselskab, Oslo, Norway Appunti@ May 21, 41932, serial No.613,836

InNorway November 21, 1931 v 'z claims. (Cisa-102) with nitric acid, insome cases after rst having been calcined; causing the lime to bedeposited inthe form of nitrate of calcium, thereafter i treating thesolution ior obtaining phosphoric acid, phosphoric salts or fertilizerproducts.

When following this process the lime may as is well known be separatedfrom the phosphoric acid andthe water present, by employing for thedissolving process nitric acid of so high concentration, that thenitrate of calcium is not dissolved. Another way proposed has been touse a diluted nitric acid and thereupon cause the deposition of thecalcium nitrate by adding concentrated nitric acid. In the latter caseinstead of addingconcentrated nitric acid the solution under treatmentmay be cooled down so far that nitrate of calcium deposits incrystalline form.

When operating in one or another way as above a@ explained great costsare incurred, concentrated nitric acid being expensive and the processhas the drawback that the apparatusemployed very soon is destroyed.Moreover the cooling process is also an expensive procedure.

The mainobit of our present inventionis to make it punible to carry outthe process of dissolving the raw phosphates by means of. nitric acid ina more economic manner than has heretofore been powble and by means of asimple An important feature of our inventlonis to so carry out thedissolving process thatl the lime is not deposited in the form ofnitrate of calcium, but in the form of a double salt composed of nitrateof calcium and ammonium, for instance 'nitrate of ammonium. Anothervaluable feature of the process lies in the fact that, according' to ourinvention we are enabled by simple 'means to separate the lime and theiron contained in the rawv material from the phosphoric acid.

By means of our improved process we are able to produce in a simplemanner nitrate products of a varying nature, suitable for fertilizerpurl u, posesf' Other features of our invention will be explained in'the vfollowing description oiii preferable specic methods of carryingout oui` invention, and in the claims.

Our invention may be carried out in the fol- 5 lowing manner. i

Raw phosphate is dissolved by means of nitric acid and to the soobtained solution is added, for' instance, ammonium nitrate. Thereby a,double salt of calcium nitrate and ammonium nitrate is l0 formed.

The crystallization of this double salt may be accelerated by addingsmall quantities of crystals oi the double salt which is to be obtained.It is possible by varying the concentration of the so- 15 A degreediierent. As a matter of course the dou- 25 ble salts, whose `solubilityunder the conditions in question is less than that of the calciumnitrate, are ordinarily of the greatest importance for the carrying outof this invention. No artiiicial cooling is required in order to havethe lime 80 separate in the form of a double salt. Even at temperaturesabove 42 (the melting point for Ca(NO3)2.4H2O). 'that is to say underconditions When Ca(NO3)2.4H2O cannot exist in solid "state at all, it ispossible to obtain a crystalliza- 35 tion of a double salt of Ca(NOa)2and NHiNOa in such quantities that the process may be utilized prohtblyin industry.

The crystallization of the double salts may, if desired, be eiectedsimultaneously with the concentration of the solution by evaporation,and this procedure greatly simplifies the process. As v will beunderstood however the crystallization may also be continued down toatmospheric temperature.

When it is desired to reduce theI solubility of the double saltsfurther, it may in some cases be suitable to add some nitric acid beforethe crystallization process takes place. 50

. Instead of adding nitrate of ammonia to the solution, the same may beformed in the solution by introducing into the same ammonia or am monia,and nitric acid; in this case the heat thereby created may be used forthe purpose of evaporating some water, and we may then also employvacuum. It will be seen from this that it may be advisable ,to usenitric acid in excess in the solution process, so much the more jas itis advantageous for dissolving some rawl phos phates to use an excess ofnitric acid.

As mentioned in the preamble, the process may following manner(reference being had also to the diagrammatic drawing annexed) z Finelycrushed calcined raw phosphate is dissolved in diluted nitric acid, thelatter being in excess of 10%. The resulting solution chiey will consistof:

The' solution is iiltered and nitrate of ammonia is added in-a suitablequantity (for instance 10-l5% of the quantity of nitrate of calcium) forvthe production of double nitrate of calciumammonium. A diluted solutioncontained about 30-40% water is thus obtained.

This dilute solution is evaporated in an appay ratus with dephlegmatorand wash-tower, down to 1820% water. Cooling the so obtained solutiondown to 20 centigrade will cause a crystallization of Sil-85% of thelime, in the form of a double salt of the formula 5 [Ca (NO3) 2.28.11]NH4NO3 Fe (P04) aHaNI-ls.

These products are ltered and washed with nitric acid, whereupon thecrystalline mass is treated with warm nitrate of lime solution, so thatthe double nitrate of calcium ammonium is dissolved and may be furthertreated in well known manner, for instance in a nitrate of lime plant.The iron-complexsalt remaining undissolved isthereupon washed and may betreated further for obtaining oxide of iron and phosphates soluble inwater.

The solution remaining after the just described crystallization.processes and still containing some lime and iron is neutralized withammonia at about 100 C., whereby the whole quantity of the remainingiron and lime is deposited in the form or phosphate of calcium andphosphate of iron. It is advisable to dilute the treated solution inorder to prevent phosphate of ammonium from crystallizing during thedeposition of dicalcium phosphate. The diluting may be eiected by meansof a solution which is. at 20-30 centigrade saturated in respect ofnitrate of ammonia and diammonium phosphate, as will be explained below.l

The above named phosphates (calcium .and

iron) are filtered and thereafter are dissolved in the wash-acidresulting from the washing out or the double nitrate of calcium-ammoniumand of the iron complex salt, and thereupon the so obtained -solution isadded to the acid solution from lime and iron are returned to theinitial solution vfor the deposition of the double salt of calciumammonium and the iron complex compound (see diagram).

In carrying out the process as a cyclic process it is possible to obtaina-quantitative separation of the content of iron and lime from the pho!-phoric acid content of the raw phosphates.

A further step in the complete. process is the following. The filtrateobtained by the just described phosphate deposition, containing monoanddiammonium-phosphate, nitrate of ammonia and water having beenneutralized with ammonia, all of the mono-ammonium-phosphate istransformed into diammonium-phosphate, after which it is cooled down to20430" centigrade. A mixture of diammonium-phosphate and nitrate ofammonia is thereby crystallized. The remaining solution containing(iO-70% nitrate of ammonia and about 1.5% diammoniumphosphate, isconcentrated and the solution is added to the acid illtrate obtained (asabove described) after the deposition of -the double salt and ironcomplex compounds at the first rieutralization with ammonia.

vacid, and adding to the so obtained solution ammonia and nitric acid,the latter in excess,

thereby causing the lime to deposit from the acid solution in the formof a double salt of nitrate of calcium and nitrate of ammonium, andseparating the deposit from the mother liquor.

2. In the treatment of phosphate materials containing viron and calciumfor obtaining therefrom products for use in industry and agriculture,the process which consists in dissolving the phosphate material innitric acid, and adding to the so obtained solution ammonium nitrate ina proportion adapted to cause the lime to deposit from the acid solutionin the form of the double salt 5(Ca(NOa)a.2aq)NH4NOa and the iron as Fe(P04) aHaNHs.

3. In thetreatment of phosphate materials containing iron and calciumfor obtaining therefrom products for use in industry and agriculture, L

the process which consists in dissolving the phosphate material innitric acid and adding to the so-obtained solution ammonium nitrate in aproportion adapted to cause the lime to deposit from the acid solutionin the form of the double salt 5(Ca(NO3)z.2aq)NH4NOa and the iron as Fe(P04) sHaNHs from products for use in industry and agriculture. Y

the process which consists in dissolving the phosphate material innitric acid, adding to the soobtained solution ammonium nitrate in aproportion adapted to cause the lime to deposit from the acid solutionin the form of the double salt 5(Ca(NO3)z.2aq)NH4NO3 and the iron asreomrsmn.-

separating this deposit from the solution whereupon the solutionremaining after the separation phate materials in nitric acid, adding tothe' so obtained solution ammonium nitrate ina proportion adapted tocause the lime to deposit from the acid solution in the form oftheIdouble salt 5(Ca(NO3)1.2aq)NH4NO3 and the iron as l Fe (P04) 3Hs.NH3,

separating this deposit from the remaining solution, neutralizing theremaining solution with ammonia, so as to deposit the remainder of limeand iron in the form of phosphates, separating these depositedphosphates and thereupon dissolving these last-named phosphates in theacid solution with which a repetition of the process is to be started,Iwhereby a cyclic process is created, securing a quantitative separationof the lime and iron of the original phosphate material from thephosphoric acid.

6. In the treatment of phosphate materials containing iron and calciumfor obtaining therefrom products for use in industry and agriculture,the process which consists in dissolving the phosphate material innitric. acid and adding to the so obtained solution ammonium nitrate ina proportion adaptcd to'cause the lime to deposit from the acid solutionin the form of the double salt 5 Ca(NOz) 2.2aq)NH4NOa and the iron asadministran, y separating thisdeposit from the solution whereupon thesolution remaining after the separation is neutralized with ammonia,thereby depositing the remainder of lime and iron in the form ofdicalcium phosphate and ferric phosphate, separating these depositedphosphates from the solution and treating the solution obtained afterthe separation of phosphates with more ammonia and thereupon cooling itto obtain diammonium-phosphate and ammonium nitrate by crystallization.

'7. In the treatment of phosphate materials containing iron and calciumfor obtaining therefrom products for use in industry and agriculture,the process which consists in dissolving the phosphate material innitric acid and adding to the obtained solution ammonium nitrate in aproportion so adapted to cause the lime to deposit from the acidsolution in the form of the double .salt

5(Ca(NOa)2.2aq)NH4NO1 and the iron as Fe(PO4)aHa.NHs.

separating this deposit from the solution whereupon the solutionremaining after the separation is neutralized with ammonia therebydepositing the remainder of lime and iron in the form of dicalciumphosphate and ferrie phosphate separating these `deposited phosphatesfrom the solution and treating the solution obtained after theseparation of phosphates with'more ammonia and thereupon cooling it toobtain a deposit of diammonium-phosphate and ammonium nitrate bycrystallization, separating this deposit, and adding the mother liquorfrom this separation to the acid ltrate obtained from the separation ofthe double salt and iron complex salt in a subsequent operation of theprocess and before neutralizing the solution with ammonia.

AN'roNIUs Foss. OLAF ODD 'r LUNDE.

